Cross-Over Nozzle System for Stack Molds

ABSTRACT

A crossover nozzle system for transferring molten plastic from an inlet at the center of the stationary platen of an injection machine to the main manifold of the molding chambers of the stack molds of the injection molding machine. The crossover nozzle system relies on molten plastic pressure within the system to actuate the primary sprue shut-off valve, and thus to open and close the flow of molten plastic to the molds. Therefore, a drool-free valve mechanism is created without needing an external actuation of the shut-off valve like, for instance, a hydraulic or a pneumatic cylinder.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation-in-part application and claimsbenefit of U.S. Continuation application Ser. No. 11/836,650, filed onAug. 9, 2007 (Attorney Docket No. 021887-000411US), which claimspriority to U.S. Non-Provisional Application No. 11/102,566, filed onApr. 8, 2005 (Attorney Docket No. 021887-000410US), which claimspriority to U.S. Provisional Application No. 60/561,053, filed on Apr.9, 2004 (Attorney Docket No. 021887-000400US), the entire contents ofwhich are herein incorporated by reference for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates to injection molding machines, and inparticular, to a system that transports molten plastic to moldingchambers of stack molds in an off-center location, or when the transferof the molten plastic needs to be in the center of the mold as in asplit sprue bar.

For injection molds having two or more cavities, it is desired to ensurethat molten plastic reaches all molding chambers at the approximatelysame time, or at least such that preferential flow to any one of themolding chambers is minimized. For most injection molds, molten plasticis transferred from the stationary machine platen to the stationary sideof the injection mold and to the molding chamber(s). For stack molds asthe one shown in FIG. 1 (prior art), molten plastic is transferredthrough the sprue, into a long sprue bar extending to the manifold,located in the center of the mold, which then transfers it equally toall cavities involved.

However, for stack molds as the ones shown in FIG. 2 (prior art) andFIG. 3 (prior art), where the centerline of molding chambers coincideswith centerline of mold, molten plastic cannot reach the manifolddirectly along the centerline, but rather must take a detour route andenter the manifold at an offset location. For such stack molds, a systemis needed to ensure a proper flow of molten plastic to the moldingchambers.

BRIEF SUMMARY OF THE INVENTION

The embodiments of the present invention provide a system that transfersmolten plastic from the inlet at the center of stationary platen ofinjection machine, through a feeder manifold and an off-center crossovernozzle, to the main manifold of the stack mold. The embodiments of thepresent invention are especially valuable when transfer of moltenplastic directly along the centerline of mold is not possible, or whenthe transfer of molten plastic is in the center of the mold as a splitsprue bar.

For a further understanding of the nature and advantages of theinvention, reference should be made to the following description takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary diagram of a prior art stack mold.

FIGS. 2-3 are exemplary diagrams of prior art stack molds where thecenterline of molding chambers coincides with centerline of the mold.

FIG. 4 is an exemplary partial view of one embodiment of a crossovernozzle system in accordance with the present invention, shown with themold closed.

FIG. 5 is an exemplary partial cross-section view of one embodiment of acrossover nozzle system, shown with sprue valve closed and mold closed.

FIG. 6 is a partial cross-section view similar to FIG. 5, shown withsprue valve open and mold closed.

FIG. 7 is a partial cross-section view of the crossover nozzle system ofFIG. 5, shown with mold open. Valves are closed on both sides, toprevent plastic leakage.

FIG. 8 is a cross-section detail of the top portion (primary side) ofthe crossover nozzle system of FIG. 5.

FIG. 9 is a cross-section detail of the central portion of the crossovernozzle system of FIG. 5.

FIG. 10 is a cross-section detail of the bottom portion (secondary side)of the crossover nozzle system of FIG. 5.

FIG. 11 is a partial cross-section through the centerline of thecrossover nozzle system of FIG. 5, along a direction orthogonal to theone shown in FIGS. 5 through 10, shown with sprue valve open and moldclosed.

FIG. 12 is a side view of the crossover nozzle of FIG. 5, shown withmold closed.

FIG. 13 is a detailed plan view of the primary side of the crossovernozzle system of FIG. 5.

FIG. 14 is a simplified plan view of the primary side of the crossovernozzle system of FIG. 5.

FIG. 15 is a detailed plan view of the secondary side of the crossovernozzle system of FIG. 5.

FIG. 16 is a simplified plan view of the secondary side of the crossovernozzle system of FIG. 5.

FIG. 17 is a partial cross-section view through the centerline of afirst alternate embodiment of the crossover nozzle system, shown withsprue valve open and mold closed.

FIG. 18 is a cross-section detail of the central portion of thealternate embodiment shown in FIG. 17.

FIG. 19 is a partial view of a second alternative embodiment of thecrossover nozzle system, shown with mold closed.

FIG. 20 is a section view of the crossover nozzle system of FIG. 19,shown with valve closed and mold closed.

FIG. 21 is an enlarged detail of the primary side of embodiment of FIG.20.

FIG. 22 is a section view of the embodiment of FIG. 20, shown with valveopen and mold closed.

FIG. 23 is a section view of the embodiment of FIG. 19, shown with moldopen for ejection of molded parts. Valve is closed on secondary side,floating portion of primary side is extended and molten plastic isretracted due to decompression of the system.

FIG. 24 is an enlarged detail of the primary side of FIG. 23.

FIG. 25 is an enlarged detail of the secondary side of FIG. 20.

FIG. 26 is an exemplary partial view of a crossover nozzle system inaccordance with a third alternative embodiment of the invention, shownwithin a closed stack mold.

FIG. 27 is a section view of the crossover nozzle system of FIG. 26,shown with mold closed and ready for injection.

FIG. 28 is an enlarged section detail of the primary side of thecrossover nozzle system of FIG. 27.

FIG. 29 is an enlarged section detail of the secondary side of thecrossover nozzle system of FIG. 27.

FIG. 30 is a section view of the crossover nozzle system of FIG. 27,shown during injection. Valve stem is retracted (valve is open) on thesecondary side, allowing transfer of molten plastic to the mainmanifold.

FIG. 31 is a section view of the crossover nozzle system of FIG. 27,shown with the mold open (between injection cycles). Valve stem isextended (valve is closed) on the secondary side, and molten plasticleft on both sides of the opening is separated from the pressurizedplastic in the flow channels.

FIG. 32 is an enlarged section detail of the central portion of FIG. 31,showing the opening of the crossover nozzle system between injectioncycles.

FIG. 33 is a section view of a crossover nozzle system in accordancewith the fourth alternative embodiment of the invention.

FIG. 34 is a section view of the crossover nozzle system of FIG. 33. Theshut-off valve closes the hole on the primary sprue shut-off insert,thus not allowing transfer of molten plastic to the molds.

FIG. 35 is an enlarged section detail of the central portion of FIG. 33,showing the different diameters on the shut-off valve.

FIG. 36 is a section view of a crossover nozzle system in accordancewith the fifth alternative embodiment of the invention.

FIG. 37 is a section view of the crossover nozzle system of FIG. 36,showing the flow of molten plastic to the molds.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIGS. 4 through 18, a stack mold that may beconfigured to use the crossover nozzle system in accordance with theembodiment of the present invention includes of a top plate 1, feederplate/stationary core plate 2, stationary core 3, stationary cavity 4,stationary cavity plate 5, stationary manifold plate 6, moving manifoldplate 7, moving cavity plate 8, moving cavity 9, moving core 10, movingcore plate 11, bottom plate 12 and crossover nozzle system 13. It shouldbe understood that fewer or more mold plates or blocks may be employeddepending on specific design requirements.

Stationary core 3 is secured to feeder plate 2, which is secured to topplate 1. Top plate 1 is bolted to stationary machine platen. Similarly,moving core 10 is secured to moving core plate 11, which is secured tobottom plate 12. Bottom plate 12 is bolted to moving machine platen.Stationary cavity 4 is secured to stationary cavity plate 5, which issecured to stationary manifold plate 6. Moving cavity 9 is secured tomoving cavity plate 8, which is secured to moving manifold plate 7.Stationary manifold plate 6 and moving manifold plate 7 are securedtogether. So, the mold has three main portions: a core side attached tothe stationary machine platen (e.g., this portion is stationary),another core side attached to the moving machine platen (this portionopens for a double stroke, once for each mold cycle), and a centralportion containing the cavity sides (which rides on the machine tie barsand opens for a full stroke, once for each mold cycle). At the end ofeach mold cycle, the mold opens equally on both sides to release themolded parts.

As used herein, the term “stack mold” refers to a two-level stack mold.However, the crossover nozzle design in accordance with the embodimentsof the present invention can be used within a three-level or afour-level stack mold, with some alteration to its configuration, butusing the same design concept as described herein. Furthermore, thecrossover nozzle system may be used in the context of a reverse-gatedstack mold, where the cores and cavities are reversed such that cavitiesare secured to machine platen portions and cores are secured to thecentral portion of the mold. In such cases, injection takes place fromthe core side, which is sometimes necessary, for example if the outerside (cavity side) of the molded article must be free of any bumps foraesthetic or functional reasons.

Shown in FIG. 5, one embodiment of the crossover nozzle system 13transfers molten plastic from feeder manifold 14 to main manifold 15through a succession of components. From feeder manifold 14, plasticenters the primary sprue bar 16 through holes 17. It continues on,through primary sprue bar extension 18, into a floating sprue 19. Fromhere, plastic is transferred into a number of spiral grooves 20 of aprimary sprue valve. Flange 22 of primary sprue bar 16, located in apocket 23 in feeder plate 2, is pressed between feeder manifold 14 onone side, and a primary pressure ring 24, also located in pocket 23, onopposite side. A pressure pad is used as backing for the feeder manifold14, in line with the crossover nozzle 13, to transfer the injectionpressures to the top plate 1. This is a safety measure designed to avoiddeflection of the manifold as can be caused by the high pressures of thecrossover nozzle system 13. Split-ring connectors 25 and bolts 26 secureprimary sprue bar extension 18 to primary sprue bar 16.

A secondary sprue 27 is installed in a pocket 28 in main manifold 15.Annular flange 29 of secondary sprue 27 is pressed between main manifold15 on one side, and a secondary pressure ring 30 on opposite side,secondary pressure ring 30 being installed in a pocket 31 in stationarymanifold plate 6. Opposite end 32 of secondary sprue 27 extends beyondsurface 33 of stationary manifold plate 6, and comes in contact withfloating sprue 19 along a spherical surface 34. A secondary spruelocating ring 35, secured in a pocket 36 on surface 33 of stationarymanifold plate 6, surrounds end 32 of secondary sprue 27 and centers itinto position. Beyond the spherical surface 34, secondary sprue 27 has acentral hole 37 in which a secondary sprue valve 38 can slide. Secondarysprue valve 38 is activated by an extension rod 39. At the opposite end,extension rod 39 has two flat surfaces 40 and is in contact with aT-coupling 41, secured to the piston 42 of a pneumatic cylinder 43.Pneumatic cylinder 43 is connected to moving manifold plate 7 through acylinder support 45, mounted onto surface 44 of moving manifold plate 7.Also mounted to moving manifold plate 7, and housed in a pocket 46 incylinder support 45, is an extension rod stop 47. Piston 42 of pneumaticcylinder 43 is always activated forward. The functioning of thiscylinder is explained below in further detail.

Primary sprue valve 21 and secondary sprue valve 38 have contact along aspherical surface 48, of equal radius as spherical surface 34. Primarysprue valve 21 and secondary sprue valve 38 are the main moving parts ofthe cross-over nozzle 13, extending/retracting once per mold cycle, toallow/restrict the flow of molten plastic from feeder manifold 14 tomain manifold 15. FIG. 6 shows the crossover nozzle system with thesprue valve extended (open). The flow of molten plastic is shown witharrows, from feeder manifold 14, through primary sprue bar 16, primarysprue bar extension 18, floating sprue 19 and primary sprue valve 21,into secondary sprue 27 and secondary sprue valve 38, which transfer itinto the main manifold 15.

FIG. 7 shows the position of crossover nozzle components when the moldis open. Both primary sprue valve 21 and secondary sprue valve 38 areclosed to prevent plastic leakage outside the system. Hatched (filled)areas represent molten plastic, present throughout the system in flowchannels and linear/spiral grooves, but sealed inside the system.

As shown in FIG. 8, the primary sprue valve 21 is activated by ahydraulic cylinder 49, mounted with bolts 50 onto surface 51 of feederplate 2. Piston 52 of hydraulic cylinder 49 has a threaded engagement 53with an activating T-coupling 54. Activating T-coupling 54 has a flangedend 55, slid into a slot 56 of an activating block 57. Extension andretraction movements of piston 52 of hydraulic cylinder 49 aretransmitted to activating block 57 through the flat-surface contactbetween flanged end 55 of activating T-coupling 54 and slot 56 ofactivating block 57. At the opposite end, activating block 57 has anextension 58 in the shape of a peg, which rides in slot 59 of a guide60. Guide 60 is secured to primary sprue bar extension 18 with bolts 61and located with tubular dowels 62. Heat transfer from heated primarysprue bar extension 18 to unheated guide 60 is minimized by the use ofan insulating plate 63 between these two components. Contact betweenextension 58 of activating block 57 and slot 59 of guide 60 helps guidethe extend/retract movement of the activating block 57, as initiated byhydraulic cylinder 49.

The side of activating block 57 facing the primary sprue bar extension18 has a slot 64. An activating lever 65, which can pivot about the axisof a dowel pin 66 secured in the body of primary sprue bar extension 18,passes through pocket 67 of primary sprue bar extension 18. End 68 ofactivating lever 65 is loosely situated in slot 64 of activating block57, being held there by a dowel pin 69 that slides in an oval slot 70 ofthe activating block 57. Opposite end 71 of activating lever 65 islocated in a matching slot 72 in the back end portion of primary spruevalve 21.

Activating block 57 has a forked extension 73 located in the spaceformed between the hydraulic cylinder 49 and primary sprue bar 16.Forked extension 73 has an oval slot 74 in which a dowel pin 75 canmove. Dowel pin 75 is installed in loose engagement in end 76 of acompression lever 77. Compression lever 77, which can pivot about theaxis of a dowel pin 78 secured in body of primary sprue bar 16, passesthrough pocket 79 of primary sprue bar 16.

When activating block 57 retracts, movement is transferred to bothactivating lever 65 and compression lever 77, causing them to pivotabout dowel pins 66 and 78 respectively (see FIGS. 6 and 8 and opensprue valves as explained below):

With reference to FIGS. 8 and 9, end 71 of activating lever 65 pushesprimary sprue valve 21 forward, which causes secondary sprue valve 38 tomove back, while staying always in contact with primary sprue valve 21,through spherical surface 48, as activated by piston 42 of pneumaticcylinder 43. As secondary sprue valve 38 moves back, away from innercone 80 of secondary sprue 27, molten plastic from spiral grooves 20 ofprimary sprue valve 21 is allowed to travel in the space formed betweenouter cone 81 of secondary sprue valve 38 and inner cone 80 of secondarysprue 27, and into linear grooves 82 of secondary sprue 27. Moltenplastic then moves from grooves 82 of secondary sprue 27 plastic movesinto linear grooves 83 of secondary sprue valve 38 and then into lineargrooves 84 of secondary sprue 27. From there, plastic is transferredinto spiral grooves 85 of secondary sprue valve 38, where it startsswirling and moves into the main manifold inlet 86. Flow line 87 of mainmanifold 15 distributes molten plastic to injection points. The reasonplastic is passed through this succession of grooves is to create apressure reducing position when secondary sprue valve 38 is closed. Assecondary sprue valve 38 closes, its cylindrical portion located betweengrooves 83 and 85 comes in contact with cylindrical portion locatedbetween grooves 82 and 84 of the secondary sprue 27. The seal-offcontact separates the high-pressure molten plastic of holes 86 and 87from the low-pressure zone of grooves 82 and 83, thus protecting cones80 and 81 from the high pressures existent in the flow channels of themold.

End 88 of compression lever 77 pushes spring washer compression pin 89forward. Spring washer compression pin 89 is installed in a central hole90 in primary sprue bar 16, and can move forward by compressing springwashers 91, installed in series and in parallel in same hole 90. Springwashers 91 transfer the compression force to the back of floating sprue19, to ensure contact of floating sprue 19 with secondary sprue 27 onspherical surface 34. Note: When end 88 of compression lever 77 releasescontact with spring washer compression pin 89, spring-back ofcompression pin 89 is controlled by dowel pin 92 secured in back end offloating sprue 19. This dowel pin passes through on oval slot 93 in thefront end of compression pin 89. Play of dowel pin 92 in slot 93 limitsthe stroke of compression pin 89.

Floating sprue 19 is loosely secured to primary sprue bar extension 18with a number of shoulder bolts 94. There is a small clearance betweenbottom of holes 95 in floating sprue 19 and beads of shoulder bolts 94,so that heads of shoulder bolts 94 do not come in contact at the backwith bottom of holes 95. This is a safety feature allowing some“floating provision” for floating sprue 19, working together withcompression provided by spring washers 91 as activated by end 88 ofcompression lever 77 and compression pin 89. This floating provision isdesigned to compensate for manufacturing tolerances and heat expansionsof the system's components.

Collector grooves and escape holes are provided in primary sprue barextension 18 and floating sprue 19 for any leaks that might happen asmolten plastic is transferred to primary sprue valve 21. Collectorgrooves 96 are provided on the inside of primary sprue bar extension 18,on both sides of inlets 97. Plastic collected by grooves 96 can bereleased through escape holes 98 connecting grooves 96 to outer wall ofprimary sprue bar extension 18. Collector grooves 99 are provided on oneside of inlets 100 only, to seal back end of floating sprue 19. Asimilar escape hole 101 is provided through wall of floating sprue 19,connecting it to escape hole 98 of primary sprue bar extension 18.

On the primary side of the crossover nozzle system 13, long cartridgeheaters 102 pass through holes in primary sprue bar 16 and primary spruebar extension 18, to hold desired temperature of molten plastic as ittravels through the crossover nozzle 13. Wires 103 from cartridgeheaters 102 pass through holes 104 in feeder manifold 14 and throughgrooves 105 in top plate 1. Similarly, on secondary side, a coil heater106 is installed around end 32 of secondary sprue 27, to keep theplastic at required melt temperature until it reaches the main manifold15. A pocket 107 is provided inside secondary sprue locating ring 35 tohouse coil heater 106. Next to pocket 107, secondary sprue locating ring35 has a small portion 108 in contact with end 32 of secondary sprue 27,for centering purpose. This is followed by a tubular shield 109,designed to direct the hot plastic towards the primary side, and preventit from squirting towards the mold operator in case of accidentalsealing failure of the crossover nozzle system 13. Wire 110 extends fromcoil heater 106, through a slot 111 at back of secondary sprue locatingring 35, into groove 112 on surface 33 of stationary manifold plate 6.

It is evident that components of the crossover nozzle 13 are preciselyoriented radially, relative to one another, so that molten plastic cantravel through the system without blockages. Dowel pin 113 locatesprimary sprue bar 16 radially in reference to feeder plate 2. Dowel pin113 passes through primary pressure ring 24, having one end press-fit ina hole 114 in pocket 23 of feeder plate 2, while opposite end is housedin an open slot 115 in flange 22 of primary sprue bar 16. Dowel pin 116orients primary sprue bar extension 18 relative to primary sprue bar 16.Shoulder bolts 94 orient floating sprue 19 relative to primary sprue barextension 18. Slot 72 of primary sprue valve 21, holding end 71 ofactivating lever 65, orients primary sprue valve 21 relative to floatingsprue 19. On opposite side, secondary sprue 27 is oriented radially,relative to main manifold 15, by dowel pin 117. One end of dowel pin 117is press-fit into a matching hole in annular flange 29 of secondarysprue 27, while opposite end is housed in an open slot 118 in mainmanifold 15. Radial orientation of all these parts ensures that inlets97 of primary sprue bar extension 18 communicate directly with inlets100 of floating sprue 19, and that inlets 100 open into grooves 119 ofprimary sprue valve 21, which direct plastic to spiral grooves 20.Plastic is then pushed, swirling, further into grooves 82 of secondarysprue 27. Radial orientation explained before matches linear grooves 82of secondary sprue 27 with linear grooves 83 of secondary sprue valve38, and also end of linear grooves 84 of secondary sprue 27 withbeginning of spiral grooves 85 of secondary sprue valve 38, so thatplastic can flow through these channels without any restrictions.

With reference to FIG. 10, at opposite end of crossover nozzle system13, a manifold sealing sleeve 120 is installed between main manifold 15and moving manifold plate 7. The purpose of this sleeve is to seal theback end of the crossover nozzle 13 from any plastic leakage from themain manifold 7. With reference to FIGS. 9 and 10, plastic from mainmanifold inlet 86 can leak through hole 121 in hole 122 around top endof manifold sealing sleeve 120, and also through the thermo-barrieraccess gap 123 inside manifold sealing sleeve 120, in groove 124 whereit can form a thermo-barrier. Any leaks from the thermo-barrier can becaught by a pair of collector grooves 125, and transferred, throughradial escape hole 126 and axial groove 127 of the manifold sealingsleeve 120, to annular groove 128 and radial escape groove 129 ofextension rod stop 47. Any plastic leaks from hole 122 can be caught bya pair of annular collector grooves 130 provided on the side of flangeportion 131 of manifold sealing sleeve 120 that faces the main manifold15. Any plastic leaks from radial escape hole 126, that are not directedby axial groove 127 out of the moving manifold plate 7, can be caught byannular groove 132 of manifold sealing sleeve 120, located below flangeportion 131. A pair of annular grooves 133 is provided on flange portion131 of manifold sealing sleeve 120, opposite grooves 130, communicating,through escape hole 134, to back of moving manifold plate 7. Plasticleaks from escape hole 134 and also from radial groove 129 are thereforedirected in the space 135 formed in pocket 46, between extension rodstop 47 and cylinder support 45.

Secondary sprue valve extension rod 39 is provided with two flatsurfaces 40 on end that is connected to pneumatic cylinder 43. Extensionrod stop 47 is held onto back of moving manifold plate 7 by cylindersupport 45, and is oriented relative to moving manifold plate 7 by dowelpin 136. Extension rod stop 47 has a round pocket 137 housing the end ofthe cylindrical portion of secondary sprue valve extension rod 39. Flatsurfaces 138 of extension rod 39 come in contact with bottom 139 ofpocket 137 when primary sprue valve 21 and secondary sprue valve 38 areopened. Bottom 139 of pocket 137 thus acts as a stroke limiter for thetwo sprue valves. Opposite end of extension rod stop 47 has anotherround pocket 140, designed with clearance, for piston 42 of pneumaticcylinder 43, and for T-coupling 41 connected to piston 42. An oval slot141 extends from pocket 137 to pocket 140 inside extension rod stop 47,guiding flat surfaces 40 of extension rod 39. With reference to FIG. 9,at opposite end, extension rod 39 has a threaded portion 142 and acylindrical surface 143, ending with a flat surface 144. Extension rod39 is threaded inside secondary sprue valve 38, and torqued until itsflat end 144 presses against flat bottom 145 of hole in secondary spruevalve 38. Correct radial orientation of secondary sprue valve 38relative to secondary sprue 27 is therefore achieved through dowel pin136, flat surfaces 40 in slot 141 and contact between surface 144 andsurface 145. It is this succession of radial orientations that locatesgrooves 83 and 85 of secondary sprue valve 38 directly in line withgrooves 82 and 84 of secondary sprue 27.

Pneumatic cylinder 43 is secured to cylinder support 45 with bolts 146.Cylinder support is secured onto surface 44 of moving manifold plate 7with bolts 147. Bottom surface 148 of pocket 46 presses onto back faceof extension rod stop 47 for support.

Extension rod 39 and T-coupling 41 are in contact, but not rigidlyconnected together. When primary sprue valve 21 pushes secondary spruevalve 38 and extension rod 39 back, piston 42 is pushed further insidepneumatic cylinder 43, until surface 138 of extension rod 39 comes incontact with bottom 139 of pocket 137 of extension rod stop 47. Piston42 of pneumatic cylinder 43 is constantly activated forward, to keepsecondary sprue valve 38 in permanent contact with primary sprue valve21. No retraction is necessary on the pneumatic cylinder; its “retract”inlet is used simply as an exhaust (FIG. 10). This means that pneumaticcylinder 43 actuates extension rod 39 and secondary sprue valve 38 onlyon the extend stroke of piston 42, until outer cone 81 of secondarysprue valve 38 is fully in contact with inner cone 80 of secondary sprue27. The force of the hydraulic cylinder 49 being stronger than that ofthe pneumatic cylinder 43, it causes the succession of componentspreviously described to push piston 42 further back in the pneumaticcylinder 43 when activating the sprue valves to open. When action of thehydraulic cylinder 49 is reversed, pneumatic cylinder 43 is relieved ofthis external force, and its own air pressure can extend piston 42 backout again. Note: Pneumatic cylinder 43 is not used at its maximumstroke. Less stroke is used, so that there is always an additionalamount of stroke available for small adjustments that might becomenecessary. For example, after extended use of the crossover nozzlesystem 13, inner cone 80 of secondary sprue 27 or outer cone 81 ofsecondary sprue valve 38 might become slightly worn. Compensation ofwear is then achieved by using additional stroke on the pneumaticcylinder 43. Such adjustment happens automatically, as piston 42 ofpneumatic cylinder 43 always tries to extend for the full stroke, butwill of course stop when inner cone 80 of secondary sprue 27 preventsouter cone 81 of secondary sprue valve 38 from going any further.

With reference to FIG. 9, secondary sprue valve 38 has a small annulargroove 149 on outer cone 81, near spherical surface 48. From this, anumber of small linear grooves 150 are provided on outer cone 81 ofsecondary sprue valve 38, extending to grooves 83. Grooves 149 and 150are designed to allow plastic caught between conical surfaces 80 and 81to escape to grooves 83 when sprue valve closes.

The crossover nozzle system 13 is synchronized with the mold cycles byuse of two signals only. These are “open” and “close” on hydrauliccylinder 49. They cause an extend/retract stroke S1 on piston 52 ofhydraulic cylinder 49, and a transferred motion/stroke S2 (equivalent toa “retract” stroke on piston 42 of pneumatic cylinder 43. The extendstroke of piston 42 is achieved by its own air pressure, which isconstantly on, therefore not requiring an additional synchronizingcontrol. An advantage of this design is that the injection machine canoperate the crossover nozzle system 13 with only one valve control.Also, precise timing between the two cylinders is not necessary, sincecylinder 43 is always pushing forward, piggybacking on the signal of thehydraulic cylinder 49. Another advantage, due to the piggyback effect,is that plastic has less chance to seep between primary sprue valve 21and secondary sprue valve 38 at spherical surface 48.

Metal o-rings are used throughout the crossover nozzle system wherevernecessary, as they can withstand high pressures and high temperatures.With reference to FIGS. 8 and 9, metal o-rings 151 are used to sealbetween primary sprue bar 16 and feeder manifold 14. Metal o-rings 152are used to seal between primary sprue bar 16 and primary sprue barextension 18. A metal o-ring 153 is also used to seal between back ofsecondary sprue 27 and pocket 28 of main manifold 15.

Dowel pins 69 and 75 are prevented from falling out of their respectiveoval slots 70 and 74 by cover plates 154 secured to the side ofactivating block 57 with button head cap screws 155.

An alternate embodiment is presented in FIG. 17, and is shown in moredetail in FIG. 18. It uses an insulating sleeve 156 and insulatingwasher 157 inserted into a central hole 158 in primary sprue bar 16, atthe interface with primary sprue bar extension 18. Insulating sleeve 156has two centering portions, 159 and 160, separated by a long relief 161.Insulating sleeve 156 is in threaded engagement 162 with body of primarysprue bar 16, and has an oval slot 163 on its front surface for torquingpurpose. Insulating sleeve 156 is be torqued until its back surfacecomes in firm contact with bottom 164 of central hole 158 of primarysprue bar 16. Insulating washer 157 is centered on the spring washercompression pin 89, between insulating sleeve 156 and back end offloating sprue 19. The insulating sleeve 156 and insulating washer 157are made of a material with low thermal conductivity, and they areemployed to protect spring washers 91 from the high heat of the primarysprue bar 16 and floating sprue 19. Radial holes 165 allow air access torelief 161, providing air insulation all around insulating sleeve 156. Anumber of flat portions 166 are provided on centering portion 160, toallow air circulation from relief 161 into space 167 formed betweencentering portion 160 and threaded engagement 162. This measureincreases length of air-cooled zone, protecting both spring washers 91and spring washer compression pin 89 from the system's high heat.

A second alternate embodiment is shown described below in conjunctionwith FIGS. 19-25. This alternate embodiment provides a system thattransfers molten plastic from the inlet at the center of stationaryplaten of injection machine, through a feeder manifold and an off-centercrossover nozzle, to the main manifold of the stack mold.

With reference to FIGS. 19 through 25, the mold comprises a top plate201, feeder plate/stationary core plate 202, stationary core 203,stationary cavity 204, stationary cavity plate 205, stationary manifoldplate 206, moving manifold plate 207, moving cavity plate 208, movingcavity 209, moving core 210, moving core plate 211, bottom plate 212 andcrossover nozzle system 213. It should be understood that fewer or moremold plates or blocks may be employed depending on specific designrequirements.

Stationary core 203 is secured to feeder plate 202, which is secured totop plate 201. Top plate 201 is bolted to stationary machine platen.Similarly, moving core 210 is secured to moving core plate 211, which issecured to bottom plate 212. Bottom plate 212 is bolted to movingmachine platen. Stationary cavity 204 is secured to stationary cavityplate 205, which is secured to stationary manifold plate 206. Movingcavity 209 is secured to moving cavity plate 208, which is secured tomoving manifold plate 207. Stationary manifold plate 206 and movingmanifold plate 207 are secured together, and supported at the center ofthe injection machine. As such, the mold has three main portions: a coreside attached to the stationary machine platen (this portion iscompletely stationary), another core side attached to the moving machineplaten (this portion opens for a double stroke, once for each moldcycle), and a central portion containing the cavity sides (which rideson the machine tie bars or guide ways and opens for a full stroke, oncefor each mold cycle). At the end of each mold cycle, the mold opensequally on both sides to release the molded parts.

With reference to FIG. 20, the crossover nozzle system 213 transfersmolten plastic from feeder manifold 214 to main manifold 215 through asuccession of components. From feeder manifold 214, plastic enters theprimary sprue bar 216 through holes 217. It continues on, throughprimary sprue bar extension 218, into a transfer chamber 219 formedbetween a back floating sprue 220 and a front floating sprue 221. Thetwo floating sprues are centered on and secured to a primary sprueshut-off valve 222. From transfer chamber 219, molten plastic travelsthrough a number of radial holes 223 to a central hole 224 in the bodyof primary sprue shut-off valve 222. From here, plastic travels intocentral hole 225 of a secondary sprue shut-off insert 226, by pushingvalve stem 227 back. Valve stem 227 is constantly activated forward,towards closing central hole 225, by a T-coupling 228, threadablysecured to the piston of an activating cylinder 229 (e.g. pneumatic).When the mold is closed for a new cycle, the injection pressure of themolten plastic overcomes the forward pressure of the activating cylinder229 and moves the valve stem 227 back. Molten plastic then gains accessto central hole 225, and from there to a number of radial holes 230extending to side grooves 231 of same secondary sprue shut-off insert226. From side grooves 231, plastic is transferred, through radial holes232, into the inlet hole 233 of the main manifold 215. Flow lines 234 ofmain manifold 215 allow transfer of molten plastic to all the moldingchambers of the mold. As the mold cycle ends, injection pressure isstopped, which allows valve stem 227 to move forward as activated bycylinder 229, and seal the secondary side of the system. On the primaryside, the floating assembly, formed by back floating sprue 220, frontfloating sprue 221 and primary sprue shut-off valve 222, moves away fromprimary sprue bar extension 218, in a manner that is described in moredetail below. Forward motion of floating assembly causes decompressionin transfer chamber 219, which results in a pullback of the moltenplastic in central hole 224. This allows a drool-free opening of thecrossover nozzle system, as the mold opens and molded parts are ejected.

Multiple heaters are used throughout the system in order to hold therequired melt temperature of the flowing plastic. On the primary side,cartridge heaters 235 are used to heat up the primary sprue bar 216 andthe primary sprue bar extension 218. On the secondary side, coil heater236 is used around the secondary sprue 237 surrounding the secondarysprue shut-off insert 226. Further components will be described below asnecessary.

The crossover nozzle system 213 is parallel to, and located at a fixeddistance in reference to the mold centerline. As can be seen from FIG.20, the main body of the crossover nozzle system 213 is stacked betweenfeeder manifold 214 and main manifold 215. Behind the feeder manifold214, in line with the crossover nozzle system 213, a pressure pad 238transfers pressures from the system, through the top plate 201, to themachine platen (injection press). This is a safety measure designed toavoid deflection of the feeder manifold 214 as can be caused by the highpressures of the crossover nozzle system 213. On the opposite side,pressures from the system are transferred through main manifold 215 toflange of manifold sealing sleeve 239 and to moving manifold plate 207.While networks of waterlines cool the mold plates, the feeder manifold214 and the main manifold 215 are heated and expand thermally.Components of the crossover nozzle system 213 are also heated andundergoing thermal expansion. The cumulation of all the individualthermal expansions along the length of the crossover nozzle systemresults in improved sealing between its components.

Aside from the slight thickness increase of the two manifolds, thermalexpansion also causes an increase in length of the manifolds, thedistance between centerline of mold and centerline of crossover nozzlebeing of special importance here. That is because this system crossessimultaneously through cooled mold plates, that have no meaningfulthermal expansion, and through the heated main manifold 215, whichexpands significantly. A number of actions are taken to stabilize thecrossover nozzle system 213 against the de-stabilizing influence of theexpanding main manifold 215:

(a) A secondary sprue locating ring 240, centered in the stationarymanifold plate 206, is employed to locate secondary sprue 273. Properlocation/centering of secondary sprue 273 enables this component to bein contact simultaneously with the expanding main manifold 215 and the“static” secondary sprue shut-off insert 226 and valve stem 227. Anyoff-center deviation of the secondary sprue 237 would cause deflectionof the valve stem 227, which could compromise the functioning of theentire crossover nozzle system.(b) Pocket 241 in the main manifold 215, holding end of secondary sprue237, is made with sufficient clearance to further prevent deviation ofthe secondary sprue 237 as would be caused by thermal expansion of themain manifold 215.(c) Pocket 242 in main manifold 215, holding one end of manifold sealingsleeve 239 is also made with sufficient clearance, to prevent anydeviation of the sealing sleeve 239, which could be transferred to valvestem 227.

By providing seal-offs and clearances as described, manifolds areallowed to expand or retract without putting stress onto components ofthe eccentric crossover nozzle system, all the while sealing on pairs ofmating surfaces transversal to centerline of crossover nozzle system.

On the primary side, the cooled feeder plate 222 centers the primarysprue bar 216, which has only planar contact with the expanding feedermanifold 214.

With reference to FIG. 21, further components will now be described. Onthe primary side, flange 243 of the primary sprue bar 216, housed in apocket 244 in feeder plate 202, is compressed between feeder manifold214 on one side and a primary pressure ring 245, also housed in pocket244, on opposite side. The primary sprue bar extension 218 is secured toprimary sprue bar 216 with split-ring connectors 246 and bolts 247. Acentral hole 248 in body of primary sprue bar 216 houses stacks ofspring washers 249, installed, with a controlled amount of compression,in parallel and in series, and centered by a spring washer compressionpin 250, housed in same central hole 248. While flanged end of springwasher compression pin 250 is backed by bottom of hole 248, opposite endhas a slot 251, shaped to allow sliding motion of a dowel pin 252,installed in fixed engagement, in back end of back floating sprue 220.Spring washers 249 are compressed between flanged end of compression pin250 and back end of back floating sprue 220, constantly exertingpressure onto back floating sprue 220, which transfers it to contactsurface between primary sprue shut-off valve 222 and secondary sprueshut-off insert 226. Back floating sprue 220 has two external portions:a back portion 253, in loose engagement in primary sprue bar 216, and afront portion 254, for centering in central hole 255 of primary spruebar extension 218. Similarly, the front floating sprue 221 has a backportion 256, for centering in central hole 257 of primary sprue barextension 218. Back portion 256 of front floating sprue 221 being largerthan front portion 254 of back floating sprue 220, the injectionpressures of transfer chamber 219 are pushing front floating sprue 221forward when injection is process. Fine thread engagement 258 betweenback floating sprue 220 and primary sprue shut-off valve 222, and finethread engagement 259 between front floating sprue 221 and primary sprueshut-off valve 222, transfer forward pressures of spring washers 249 andof transfer chamber 219 to the contact surface 260 between primary sprueshut-off valve 222 and secondary sprue shutoff insert 226. Also, anumber of axial, peripherally acting forces are present around thesystem. These are provided by compression springs 261, installed with acontrolled amount of compression, around spring guide pins 262,threadably engaged in the back of the flange portion 263 of frontfloating sprue 221. Compression springs 261, backed by fixed primarysprue bar extension 218, put constant pressure forward onto the back ofthe flange portion 263 of the front floating sprue 221. When mold opensto allow ejection of molded parts, the floating assembly is pushed awayfrom the primary sprue bar extension (as previously mentioned) bycompression springs 261. In conclusion, there are 3 sets of forwardforces/pressures that transfer to surface of contact 260 between primaryand secondary sides: the force of spring washers 249, the force ofpressurized transfer chamber 219 (when plastic is injected), and theforces of compression springs 261. The axial motion freedom of thefloating assembly is allowed by shoulder bolts 264, which connect flangeportion 263 of the front floating sprue 221 in axial sliding contactwith primary sprue bar extension 218.

Sealing means are provided throughout the system to prevent plasticleaks. On the primary side, metal seals 265 are installed in groovesaround holes 217 at the contact surface between primary sprue bar 216and feeder manifold 214. Metal seals 266 are also used to seal holes 217between primary sprue bar 216 and primary sprue bar extension 218. Bothback floating sprue 220 and front floating sprue 221 have thin annularprofiles, 267 and 268 respectively, extending into transfer chamber 219.As transfer chamber 219 is filled, thin profiles deflect slightly underinjection pressure, creating metal-to-metal sealing against holes 255and 257. A back seal 269, held in place by a spacer 270, surroundsportion 253 of back floating sprue 220, to act as backup for seal ofthin profile 267 against central hole 255. A front seal 271, held inplace by a clamp ring 272 secured with bolts 273 to primary sprue barextension 218, is used as backup seal between front floating sprue 221and primary sprue bar extension 218. Both back seal 269 and front seal271 can be made of a composite material, with high thermal resistance.On the secondary side, a metal seal 274 is used around inlet hole 233 ofmain manifold 215, to seal around secondary sprue 237 (see FIG. 25).

As shown in FIG. 25, on secondary side, flange 275 of secondary sprue237 is pressed between main manifold 215 and a secondary pressure ring276, installed in a pocket 277 in stationary manifold plate 206. Onopposite side of main manifold 215, manifold sealing sleeve 239 havingflange portion 278 pressed between main manifold 215 and moving manifoldplate 207, seals against plastic leaks from the inlet hole 233, both atthe bottom of pocket 242 and on both sides of flange 278. Manifoldsealing sleeve 239 has a number of annular grooves 279 placed on theinside, outside, and on both sides of flange portion 278, which act ascollector grooves for any leaks, directing them safely out of thesystem.

On surface 280 of moving manifold plate 207, a cylinder support 281 issecured with bolts 282 and located with dowel pins 283. Activatingcylinder 229 is secured to cylinder support 281 with bolts 284. A valvestem stop 285 is located with dowel pins 286 in clearance pocket 287inside cylinder support 281. Top surface 288 of valve stem stop 285 ispressed against surface 289 of cylinder support 281.

As previously mentioned, molten plastic flows through central hole 225of secondary sprue shut-off insert 226, to reach radial holes 230, bypushing valve stem 227 back. Valve stem 227 is pushed back until flatsurfaces 290 machined close to its back end (end which is in contactwith T-coupling 228) come in contact with flat surfaces 291 of valvestem stop 285. A safety feature designed to protect the activatingcylinder 229 from repeated shocks is provided by the positive stop ofsurfaces 290 on 291 takes place before piston of cylinder 229 reachesthe end of its stroke. The shocks caused by injection pressures on valvestem 227 are transferred to surfaces 291 and not to activating cylinder229. Furthermore, no retraction signal is necessary on activatingcylinder 229; its “retract” inlet is used only as an exhaust. Anadvantage of the embodiment of FIGS. 19-25 is that it doesn't requiresynchronization with mold cycles.

With reference to FIG. 21, radial cooling holes 292 are provided throughprimary sprue bar 216, to allow air cooling of spring washers 249 inorder to extend the life of these components.

The crossover nozzle system in accordance with the embodiments of thepresent invention has the following unique and advantageous features:

1. The crossover nozzle system is provided with two, symmetricallyplaced, inlet holes in the primary sprue bar, which are connectedcentrally to the transfer chamber in the primary sprue bar extension.Such symmetry allows central placement, around a singular axis, of allthe components of the crossover nozzle system.2. By removing shoulder bolts at the front of the primary side, theentire floating assembly, complete with spring washers and compressionpin, can be removed from the crossover nozzle system for servicing,while mold in still in the injection press. This feature allowsadjustments of the spring washers, alterations of their configuration,and modifications of the spring washer compression pin in order tomodify the force output, without requiring removal of the entirecrossover nozzle system from the mold. It is possible to increase ordecrease the force output and deflection of the spring washers byaltering their configuration. For example, stacking spring washers inparallel increases the force output, while stacking them in seriesincreases the deflection.3. During plastic injection, a substantial increase to the force outputof spring washers is provided by the injection pressure of moltenplastic in the transfer chamber between back floating sprue and frontfloating sprue, due to the outer size differential between back floatingsprue and front floating sprue.4. The thin annular profiles of the back floating sprue and the frontfloating sprue extending into the transfer chamber use the very force ofinjection as sealing means. These profiles are sufficiently thin toallow deflection and create metal-to-metal sealing all around walls ofcentral holes of primary sprue bar extension.5. A back seal and a front seal, which can be made of a differentmaterial (non-metal), are provided as backup for the metal-to-metalseals around transfer chamber.6. The crossover nozzle system as described is adaptable to various moldheights. Adaptability is achieved by altering the length of the primarysprue bar. The primary sprue bar extension and the rest of thecomponents of the crossover nozzle system will not need alterations.7. When the mold opens and the floating assembly extends from theprimary side, the thin annular profile of the back floating sprue actsas a shut-off surface against inlet holes opening into the transferchamber. The transfer chamber is thus sealed from the inlet holes, tofurther prevent drooling until the system closes for a new mold cycle.8. Being made of three main components, the floating assembly has theadvantage of bringing different material characteristics to differentrequirement areas. The back floating sprue can be made of an alloy hardenough to withstand the forces of the spring washers, but soft enoughnot to score the inner walls of the primary sprue bar extension. Thefront floating sprue can be made of an alloy soft enough to avoidscoring the inner walls of the primary sprue bar extension, but havinghigh thermal conductivity to allow proper heat transfer from cartridgeheaters of the primary sprue bar extension to the front end of theprimary sprue shut-off valve. The primary sprue shut-off valve is madeof a high-hardened alloy, to withstand the constant beating at thecontact surface with secondary sprue shut-off insert.9. By unclamping the top plate from the stationary platen, withassistance of a hoist, the entire mold can be moved over (attached tothe moving platen) for servicing the heaters in the injection machine.10. Secondary side shut-off valve does not require a synchronizingsignal from the mold, due to the constant forward action of thepneumatic cylinder. Such a design simplifies the construction andfunctionality of the system considerably, as the valve stem seals theopening on the secondary side automatically when decompression takesplace, before the mold opens.11. The secondary sprue shut-off insert separates the flow of moltenplastic into multiple channels, then re-connects them as they enter theinlet of main manifold. Such a design creates a swirling motion of themolten plastic, washing off the inlet hole of the main manifold toprevent formation of dead spots (stale plastic).12. The valve stem and the entire secondary side of crossover nozzlesystem can also be serviced while the mold is in the injection press.

A third alternate embodiment is shown described below in connection withFIGS. 26-32. According to one aspect of the third alternative embodimentof the present invention, the crossover nozzle system is a leak-proofmechanism that transfers molten plastic from the inlet at the center ofthe stationary platen of an injection machine, through a feedermanifold, to a main manifold of the stack mold, utilizing the injectionpressures existent throughout the system and the thermal expansion ofits various components to create a leak-proof seal.

Furthermore, according to another aspect of the third alternativeembodiment of the present invention, the off-center crossover nozzlesystem has a primary side (attached to the stationary portion of thestack mold) and a secondary side (attached to the central portion of thestack mold), both sides of the system having movable componentsactivated to close off the flow of molten plastic after each injectioncycle. Activation of movable components is automatically timed inrelation to the mold cycles without the use of dedicated synchronizingequipment, by way of preloaded springs and internal and externalcylinders actuated continuously towards extending the movablecomponents.

Yet another feature of this third alternative embodiment of the presentinvention, provides an hourglass portion (or other convergent-divergentprofile) on both the primary and secondary sides of the crossover nozzlesystem, adjacent to their contact surface. Both hourglass portions arecooled by way of surrounding cooling circuits fed from the mold orexternally from the machine. Cooling causes formation of skins ofsolidified plastic inside hourglass portions after each injection cycle.These skins substantially reduce the size of hourglass holes prior tomold opening to prevent drooling. Upon start of new cycle, newlyinjected plastic melts the skins on both sides of the opening, so thatboth hourglass portions are restored to their real sizes and flow ofmolten plastic goes on unrestricted.

These feature enable the crossover system to provide a leak-proof,off-center system that transfers molten plastic from the inlet at thecenter of the stationary platen of an injection machine to the mainmanifold located in the central portion of the stack mold. Furthermore,these features provide a crossover nozzle system having a drool-freeopening to avoid spills and waste. In addition, these features provide acrossover nozzle system that achieves effective sealing of its openingfrom the pressurized flow channels to prevent plastic leaks.

Referring to FIG. 26, a stack mold in accordance with the inventioncomprises a top plate 1100, feeder plate/stationary core plate 1102,stationary core 1104, stationary cavity 1106, stationary cavity plate1108, stationary manifold plate 1110, moving manifold plate 1112, movingcavity plate 1114, moving cavity 1116, moving core 1118, moving coreplate 1120, a bottom plate 1122 and a crossover nozzle system 1124. Itshould be understood that fewer or more mold plates or blocks may beemployed depending on specific design requirements.

As is typical of stack molds, the embodiment shown in FIG. 26 presentsthree main mold portions. A stationary core portion, secured onto thestationary machine platen, comprises top plate 1100, feeder plate 1102and stationary core 1104. Similarly, a moving core portion, secured ontothe moving machine platen, comprises bottom plate 1122, moving coreplate 120 and moving core 1118. A central mold portion comprisesstationary cavity 1106, stationary cavity plate 1108, stationarymanifold plate 1110, moving manifold plate 1112, moving cavity plate1114, moving cavity 1116 and all connecting components therein. Thestationary core portion is completely stationary; the moving coreportion opens for a double stroke, once per mold cycle, and the centralportion, which rides on the machine tie bars or guide ways, opens for afull stroke, once per mold cycle. After each mold cycle, the moldportions move as described to release the molded parts, resulting inequal opening strokes on both sides of the central portion.

With reference to FIG. 27, crossover nozzle system 1124 transfers moltenplastic from a feeder manifold 1126 to a main manifold 1128 through asuccession of components. From feeder manifold 1126, plastic enters aprimary sprue bar 1130 through a number of symmetrically placed holes1132. It continues on, through primary sprue bar extension 1134, into atransfer chamber 1136 formed between a back floating sprue 1138 and theback portion of a front floating sprue 1140, connected by threadedengagement. A primary sprue shutoff insert (or valve) 1142, installed inthreaded engagement at the front end of the front floating sprue 1140,directs molten plastic into a secondary sprue shutoff valve (or insert)1144 of the secondary side of the crossover nozzle system 124, bypushing back a valve stem 1146. When valve stem 1146 is pushed backfully (as shown in FIG. 30), molten plastic gains access to a number ofside grooves 1148 formed between secondary sprue shutoff valve 1144 anda surrounding secondary sprue 1150, and is directed to an inlet hole1152 of main manifold 1128, and to flow channels 1154 thereon, to reachall the injection chambers of the mold. Further components and featuresare presented below.

When the mold is closed and injection is in process, the crossovernozzle system is pressed between feeder manifold 1126 and main manifold1128. A pressure pad 1156, located behind the feeder manifold 1126, inline with crossover nozzle system 1124, and a manifold sealing sleeve1158, located behind the main manifold 1128 in surrounding relation tothe valve stem 1146, allow transfer of injection pressures of thecrossover nozzle system 1124 back to the mold plates and to theinjection machine. The injection pressures present in the system and thethermal expansions of the various components work together to achieve animproved seal throughout the system and at the contact surface “A”between the primary and the secondary sides of the crossover nozzlesystem 1124. In addition, several other features are provided to achievean improved seal and a drool-free opening at the end of each mold cycle,as described in detail below.

Referring to FIG. 27 and FIG. 28, in a central pocket 1160 of theprimary sprue bar 1130 are stacked several sets of spring washers 1162.Spring washers shown are Belleville type, which are especially suitedfor high loads in small spaces. They are installed in a sequence ofseries and parallel, and are centered on a spring washer compression pin1164. During injection, head of compression pin 1164 rests againstbottom of pocket 1160, transferring injection pressures back to theinjection machine. The opposite end of compression pin 1164 is securedto back end of back floating sprue 1138 in a loose connection, slidablefor a short distance by way of a dowel pin 1166 and slot 1168. Springwashers 1162 are installed with a controlled amount of preload, to urgethe floating assembly (formed by back floating sprue 1138, frontfloating sprue 1140, primary sprue shutoff insert 1142 and all theirconnecting components therein) against the secondary sprue shutoff valve1144 at contact surface “A”. The number of spring washers 1162 and theirinstallation sequence can be varied to modify their force output ortheir deflection as desired (optionally, a spacer 1170 can be installedbehind the spring packs). The stacking of spring washers in seriesincreases the deflection in proportion to the number of washers, theload remaining the same as with a single washer. Stacking of springwashers in parallel increases the load (the force output), theoreticallyin proportion to the number of washers; however, practically this is notentirely true, since friction between washers creates an apparenthysteresis in the load-deflection curve. More information on springwashers is provided in technical catalogues of various manufacturers,which are commercially available.

Another extension force urging the floating assembly against thesecondary side at contact surface “A” is provided by a number ofcompression springs 1172, installed circumferentially between primarysprue bar extension 134 and back of front floating sprue 1140.Compression springs 1172 are installed with a controlled amount ofpre-compression, to automatically activate the floating assembly forwardas soon as the mold starts to open, similar to spring washers 1162.

A built-in pneumatic cylinder 1174, located behind the floatingassembly, provides yet another extension force urging the floatingassembly against the secondary side. A clamp ring 1176, threadablysecured to primary sprue bar extension 1134, is located in pocket 1178formed at the back of front floating sprue 1140. An annular groove 1180at the back of clamp ring 1176 directs pressurized air from an airsupply 1182 to a number of circumferential holes 1184 connecting tobottom of pocket 1178. A combination of inner and outer seals preventsair escape from pocket 1178. Pressurized air is supplied continuously topneumatic cylinder 1174, such that it automatically activates thefloating assembly to extend as soon as mold starts to open. A benefit ofsuch a design is that no additional system is required to synchronizethe pneumatic cylinder with the mold cycles. Shoulder bolts 1186 limitthe stroke of the floating assembly, while also acting as guide pins forcompression springs 1172.

As soon as injection stops and mold starts to open, the floatingassembly extends under the combined influence of the spring washers1162, compression springs 1172 and built-in pneumatic cylinder 1174.These three features have a double role: to hold the floating assemblyfirmly pressed against the secondary side of the system during injectionfor a leak-proof process and to automatically extend the floatingassembly as soon as the mold start to open, to seal flow channels andprevent drooling.

As can be seen in FIG. 28, back floating sprue 1138 has a pair ofannular grooves 1188 behind transfer chamber 1136, while back end offront floating sprue 1140 has a thin annular extension 1190. Annulargrooves 1188 collect any plastic leaks behind the transfer chamber 1136,while thin annular extension 1190 can flex slightly under injectionpressure to achieve circumferential contact with front central hole 1192of primary sprue bar extension 1134, creating a metal-to-metal seal atthe front of transfer chamber 1136. A back seal 1194, held in place by aspacer 1196, surrounds the back end 1198 of back floating sprue 1138, toact as backup for seal of annular grooves 1188. A front seal 1200, heldin place by clamp ring 1176, is used as backup for metal-to-metal sealof thin annular extension 1190.

Front central hole 1192 is larger than back central hole 1202 of primarysprue bar extension 1134, as can be seen clearly in FIG. 28. Thisdiametric difference uses the injection pressure to further push thefloating assembly forward for a leak-proof seal at contact surface “A”.

The floating assembly stroke allowed by shoulder bolts 1186 is designedsuch that, when floating assembly is fully extended, the back end 1198of back floating sprue 1138 completely covers inlet holes 1204connecting to transfer chamber 1136. This separates the plastic left inthe transfer chamber 1136 and in the front central holes 1206 (of backfloating sprue 1138) and 1208 (of front floating sprue 1142) from thepressurized plastic of inlet holes 1132 and 1204, achieving a pressurereduction at the front of the primary side of the system. Extension offloating assembly also achieves a pullback of the plastic left incentral holes 1206 and 1208, to reduce drool as the system opens.

With reference to FIGS. 28 and 30, primary sprue shutoff insert 1142 andsecondary sprue shutoff valve 1144 have yet another feature designed toreduce drool of molten plastic during mold opening. Central hole 1208 ofprimary sprue shutoff insert 1142 and central hole 1210 of secondarysprue shutoff valve 1144 are provided with hourglass (or otherconvergent-divergent profiles) portions 1212 and 1214 respectively.Cooling circuits 1216 and 1218, fed externally from the mold or theinjection machine, surround the hourglass portions to achieve cooling ofthe plastic left in holes 1208 and 1210 during mold opening. Thisplastic solidifies partially, forming skins 1220 and 1222 inside thehourglass portions, as shown in FIG. 32. The skins reduce the hourglassholes considerably, which further helps prevent drooling. As moltenplastic is forced through the system for a new cycle, its hightemperature helps melt the solidified skins, which are then reused,preventing formation of stale plastic in the system.

On the secondary side of the crossover nozzle system 1124, an activatingcylinder 1224 (e.g. pneumatic) is secured onto a cylinder support 1226,itself mounted onto the stationary manifold plate 1112. Piston 1228 ofactivating cylinder 1224 is continuously activated to extend (the“extend” function is always on). The “retract” function of the cylinderis not used; the “retract” inlet works only as an exhaust. A T-coupling1230, threadably engaged to piston 1228, is in loose connection withback end of valve stem 1146. T-coupling 230 and valve stem 1146 are notmechanically secured; that is not necessary since the “retract” functionof the cylinder is not used and piston 1228 does not retract valve stem1146. They are however maintained in contact, either by piston 1228extending to close the valve, or by injection pressure pushing valvestem 1146 back to open the valve. Valve stem 1146 is pushed back untilit bottoms out in pocket 1232 of cylinder support 1226. To protect theactivating cylinder 1224 from damage due to repeated shocks, valve stem1146 bottoms out in pocket 1232 before piston 1228 reaches the end ofits stroke.

When injection pressures push valve stem 1146 back, molten plastictransferred through central holes 1208 and 1210 gains access to radialholes 1234, then to side grooves 1148 and, through radial holes 1236, toinlet hole 1152 of main manifold 1128. Any plastic leaks from inlet hole1152 are collected by a number of annular grooves 1238 located on bothsides of flange portion and on the inside and outside of manifoldsealing sleeve 1158, and are drained externally.

Back seal 1194 and front seal 1200 can be made of a composite material,with high thermal resistance. Furthermore, a high-temperature seal 1240is provided on back end 1198 of back floating sprue 1138, to act asbackup for back seal 1194. On the primary side, high-temperature seals1242 and 1244 seal around cooling circuit 1216, and a pair ofhigh-temperature seals 1246 prevents air escape between front floatingsprue 1140 and clamp ring 1176 from built-in pneumatic cylinder 1174. Onthe secondary side, high-temperature seals 1248 and 1250 seal aroundcooling circuit 1218.

Flow of molten plastic through the various components of the crossovernozzle system 1124 is sealed with metal o-rings, which are resistant toboth high temperatures and high-pressures. With reference to FIG. 28, onthe primary side holes 1132 are sealed by metal o-rings 1252 (betweenfeeder manifold 1126 and primary sprue bar 1130) and metal o-rings 1254(between primary sprue bar 1130 and primary sprue bar extension 1134).With reference to FIG. 29, on the secondary side metal o-ring 1256,located between secondary sprue 1150 and main manifold 1128, sealsaround inlet hole 1152.

An advantage of the embodiments of the present invention, from a moldoperator's point of view, is that it allows servicing of the crossovernozzle system with little effort, while the mold remains in the machine.Removal of shoulder bolts 1186 allows the operator to simply pull outthe entire floating assembly, complete with spring washers 1162 andcompression pin 1164, while the primary sprue bar extension 1134 remainsattached to the primary sprue bar 1130; this is useful since it givesthe operator quick access to spring washers 1162 for any desiredadjustments. Another advantage is that the length of the crossovernozzle system can be varied depending on mold stack height, withoutreplacing the entire crossover nozzle system. As an example, the primarysprue bar extension 1134, floating assembly and secondary side can stayunchanged, while only the length of primary sprue bar 1130 can bevaried. This is made possible by split-ring connectors 1258, which inthe example shown are two halves of a connector ring; removal of bolts1262 allows detachment of primary sprue bar extension 1134 from primarysprue bar 1130.

The primary side of the crossover nozzle system is heated by way ofcartridge heaters (not shown in the drawings), as described above. Thesecondary side of the system is heated by a coil heater (not shown inthe drawings), which is housed in a secondary sprue locating ring 1260,found in surrounding relation to secondary sprue 11150, similar to thatdescribed above.

The crossover nozzle system in general and that of the third alternativeembodiment described above provides the following advantageous features:

1. The built-in pneumatic cylinder of the primary side of crossovernozzle system provides a positive extension force urging the floatingassembly to extend as soon as secondary side is retracted from contactat surface “A”.2. Continuous supply of pressurized air to built-in pneumatic cylinder(described at 1 above) achieves appropriate release (extension) of thefloating assembly after each mold cycle, without use of any additionaltiming systems to synchronize the extension of floating assembly withthe opening of the mold.3. Extension of the floating assembly to its full stroke achievessealing between the transfer chamber and the inlet holes, resulting in apressure reduction at the front of the primary side of the system.4. Extension motion of the floating assembly causes a pullback of theplastic left in the central hole of the primary sprue shutoff insert, toprevent plastic drool.5. The design of primary side of the crossover nozzle system allowsquick and easy removal of the floating assembly for service, while moldremains in the injection machine.6. The two-piece design, having a back floating sprue and primary sprueshutoff insert, allows machining of hourglass portion (or otherconvergent-divergent profiles) at the front of the primary side of thesystem.7. Cooling around the hourglass portion (or other convergent-divergentprofiles) of the central hole of primary sprue shutoff insert causesformation of a skin that reduces size of hourglass hole, thus helpingprevent plastic drool. Furthermore, with each new mold cycle, the newlyinjected plastic melts the existing skin and reuses it, to preventformation of stale plastic.8. The activating cylinder of the secondary side of the crossover nozzlesystem provides a continuous extension force urging the valve stem toclose the valve as soon as injection stops.9. The continuous supply to the “extend” inlet of the activatingcylinder (described at 8 above) achieves appropriate release (extension)of the valve stem at the end of each mold cycle, without use of anadditional timing systems to synchronize the extension of valve stemwith the opening of the mold.10. The extension of the valve stem separates the central hole of thesecondary sprue shutoff valve from the pressurized plastic of the sidegrooves and the radial holes, achieving a pressure reduction at thefront central hole to reduce plastic drool during opening of mold.11. Cooling around the hourglass portion (or other convergent-divergentprofiles) of the central hole of secondary sprue shutoff valve causesformation of a skin that reduces size of hourglass hole, thus helpingreduce plastic drool. Furthermore, with each new mold cycle, the newlyinjected plastic melts the existing skin and reuses it, to preventformation of stale plastic.12. The crossover nozzle system as described is adaptable to variousmold heights. Adaptability is achieved by altering the length of theprimary sprue bar. The primary sprue bar extension, the floatingassembly and the secondary side of the crossover nozzle system may notneed to be altered.13. The crossover nozzle system described is not limited to a 2-levelstack mold. It can be adapted to 3-level and 4-level stack molds byutilizing different design configurations, while maintaining the overallconcept of crossover nozzle system.

A fourth alternate embodiment of the invention is described below inconnection with FIGS. 33-35. According to one aspect of the fourthalternative embodiment, the crossover nozzle system relies on moltenplastic pressure within the system to actuate the primary sprue shut-offvalve, and thus to open and close the flow of molten plastic to themolds. The primary sprue shut-off valve (hereinafter the shut-off valve)moves to an open position when the molten plastic pressure is highenough to overcome the biasing force of a spring or other urging meanswhich biases the shut-off valve toward the closed position. When themolten plastic pressure drops, the biasing force overcomes the pressureforce, and the shut-off valve moves to the closed position, i.e. the tipof the valve closes the opening on the primary sprue shut-off insert.Therefore, a drool-free valve mechanism is created without needing anexternal actuation of the shut-off valve like, for instance, a hydraulicor a pneumatic cylinder.

Furthermore, an effective sealing is provided by the high pressure ofthe molten plastic against the tapered extension of the back floatingsprue sleeve and the tapered extension of the front floating sprue. Whensubjected to the high pressure of the molten plastic, the taperedextensions attempt to deform outwards, but their deformation is arrestedby the adjacent primary sprue bar, thus creating a metal-to-metalsealing when a good sealing is needed the most, i.e. when the moltenplastic pressure inside the crossover nozzle system is high. A backseal, which may be a wiper seal, is provided between the back floatingsprue sleeve and the primary sprue bar to further reduce leaks of themolten plastic between these parts. The molten plastic that still leakspast the seals is drained out of the crossover nozzle system through theweep holes.

Yet another feature of this fourth alternative embodiment of the presentinvention is a reduced recirculation flow of the molten plastic in thespace between the front floating sprue insert and back floating spruesleeve, because the larger diameter of the front floating sprue insertreduces the space available for the molten plastic recirculation.

Moreover, the disassembly of the crossover nozzle system is simplifiedby using a two-part “C” clamp design. The clamp attaches with the frontfloating sprue using one securing screw per each part of the “C” clamp.Removal of the “C” clamp enables easy removal of the front floatingsprue insert, front floating sprue, and primary sprue shut-off inserttogether with the shut-off valve, thus providing an easy access to theparts that tend to be the most exposed to a wearout. Additionally, thesystem has a single sprue bar, i.e. the primary sprue bar, which may bean improvement compared to the systems that require both a primary spruebar and an extension sprue bar.

These features enable the crossover nozzle system to transfer moltenplastic to the molds using a single sprue bar. The system does notrequire an external source of the shut-off valve actuation, whileproviding a drool-free opening to avoid spills and waste. Theundesirable recirculation flow area is also reduced. Furthermore, thesystem is easy to assemble and disassemble using a two-part “C” clamp.In addition, the system reduces plastic leaks using the metal-to-metalseals and wiper seals.

FIG. 33 shows crossover nozzle system 1300 in accordance with the fourthembodiment of the invention. Other parts of the molds, like the topplate, feeder plate/stationary core plate, stationary core, moldcavities, manifold plates, cavity plates, core plates, bottom plates,etc., are described in connection with the other embodiments disclosedin this application, and are not shown in FIG. 33. Furthermore, while asingle crossover nozzle assembly is shown in FIG. 33, it would be clearto a person skilled in the art of injection molding that multiplecrossover nozzle assemblies may be used, both in a central and theoff-center positions.

Referring to FIG. 33, molten plastic enters crossover nozzle systemthrough holes 1324 on primary sprue bar 1310. Compression pin 1350 ispositioned in a central hole of a one-piece primary sprue bar 1310.Shoulder bolt 1314 connects compression pin 1350 with primary sprue bar1310. Spring washers 1352 are installed with a controlled amount ofpreload, to urge the floating assembly (formed by back floating sprue1303, front floating sprue insert 1322, primary sprue shut-off insert1344, and all their connecting components) against spring 1326, which,in turn, biases shut-off valve 1346 towards opening 1354 in primarysprue shut-off insert 1344. When the tip of shut-off valve 1346 pressesagainst opening 1354, the flow of molten plastic toward the molds isclosed. This is the position shown in FIG. 33. The counter-force thatbiases shut-off valve 1346 away from opening 1354, thus opening the flowof molten plastic toward the molds, can be provided by the pressure ofthe molten plastic itself, as explained below with reference to FIG. 35.

Referring still to FIG. 33, the molten plastic which passes throughinlet holes 1324 enters transfer chamber 1370 disposed between frontfloating sprue insert 1322 and primary sprue bar 1310, and furtherenters radial holes 1356 and the space between shut-off valve 1346 andprimary sprue shut-off insert 1344. Back tapered extension 1320 on backfloating sprue sleeve 1302 prevents molten plastic from leaking in thedirection of compression pin 1350, while front tapered extension 1328 onfront floating sprue 1338 prevents molten plastic from leaking in thedirection of primary sprue shut-off insert 1344. Due to the highpressure of molten plastic, front tapered extension 1328 and backtapered extension 1320 bend outwardly radially, i.e. away from themolten plastic and in the direction of primary sprue bar 1310. However,due to the mechanical strength of primary sprue bar 1310, the bending isarrested and a metal-to-metal seal is created, thus preventing moltenplastic leakage between back floating sprue sleeve 1302 and primarysprue bar 1310 (in the direction of compression pin 1350) or frontfloating sprue 1338 and primary sprue bar 1310 (in the direction ofprimary sprue shut-off insert 1344). Back seal 1301 may be disposedbetween primary sprue bar 1310 and back floating sprue sleeve 1302 tofurther reduce any molten plastic leaks past the metal-to-metal seal.Back seal 1301 may be a wiper seal having an advantage of expandingoutwardly when subjected to high temperature, thus further increasingthe pressure between the seal and surrounding material, which, in turn,decreases the leakage of molten plastic. The molten plastic that stillleaks past back seal 1301, and enters the space between back floatingsprue 1303 and primary sprue bar 1310 or the space around spring washers1352, may be discharged out of the system by one or more weep holes1316. Additionally, molten plastic that leaks past the metal-to-metalseal between front floating sprue 1338 and primary sprue bar 1310 isfurther sealed off by front seal 1334.

FIG. 33 also shows a two-part “C” clamp 1336, which is attached withfront floating sprue 1338 by fasteners 1340, which may be securingscrews. Removal of “C” clamp 1336 enables an easy access to primarysprue shut-off insert 1344 and further to shut-off valve 1346. Thoseparts may be susceptible to wearout and, therefore, may require morefrequent servicing or replacement.

The actuation of shut-off valve 1346 is shown with reference to FIGS. 34and 35. FIG. 34 shows the path of molten plastic (depicted by theshading) through crossover nozzle system 1300. A second end of shut-offvalve 1346 is engaged against opening 1354 on primary sprue shut-offinsert 1344, thus preventing molten plastic from escaping toward themolds. FIG. 35 shows a detail of crossover nozzle system 1300. Biasingmeans 1326, which may be a spring, may be housed in a central opening offront floating sprue insert 1322. Biasing means (hereinafter spring)1326 are configured to engage with a first end of shut-off valve 1346,and to bias the valve toward opening 1354 (not shown) on primary sprueshut-off insert 1344. Shut-off valve 1346 has a non-uniform diameter:bigger diameter D₂ on the side closer to spring 1326 (the first end),and a smaller diameter D₁ on the side closer to opening 1354 (the secondend). As the high pressure molten plastic enters the space betweenshut-off valve 1346 and front floating sprue insert 1322, the differencebetween shut-off valve 1346 diameters D₂ and D₁ results in a projectionarea for the upwardly pushing pressure of molten plastic (in thedirection of spring 1326). This projection area, when multiplied withthe high pressure of molten plastic, is enough to overcome the biasingforce of spring 1326 and to move shut-off valve 1346 toward spring 1326.The movement of shut-off valve 1346 toward spring 1326 removes thesecond end of shut-off valve 1346 from opening 1354, thus allowingmolten plastic to flow toward the molds. The compression of spring 1326may stop when shank 1360 on shut-off valve 1346 makes contact with frontfloating sprue insert 1322, thus creating a metal-to-metal seal whichprotects spring 1326 from molten plastic. When the pressure of themolten plastic is reduced by, for example, stopping the molten plasticfeed drive (not shown), the biasing force of spring 1326 becomes higherthan the opposing pressure force. Consequently, spring 1326 now movesshut-off valve 1346 to contact hole 1354, thus shutting off the flow ofmolten plastic to the molds. Therefore, shut-off valve 1346 is actuatedbased on the pressure of molten plastic. No external actuator, like, forexample a pneumatic or hydraulic cylinder, is needed for opening andclosing of the flow of molten plastic to the molds.

Referring still to FIG. 35, as molten plastic leaves inlet holes 1324, arecirculation zone R may be created in the space between front floatingsprue insert 1322 and back floating sprue sleeve 1302. A recirculationflow is undesirable, because molten plastics may cool inside the zone,and may start solidifying. The size of the recirculation zone is reducedin crossover nozzle system 1300 by increasing the diameter of frontfloating sprue insert 1322 in the area of back tapered extension 1320.

The crossover nozzle system in general and that of the fourthalternative embodiment described above provides the followingadvantageous features:

1. Primary sprue bar is one-piece. Primary sprue bar extension is notused, thus a design simplification is achieved.2. The shut-off valve actuation is achieved by molten plastic pressureand the non-uniform diameter of the shut-off valve, thus not requiringan external actuator like, for example, a pneumatic or hydrauliccylinder.3. When the pressure of molten plastic is reduced, the spring thatbiases the shut-off valve pushes the shut-off valve into contact withthe hole on the primary sprue shut-off insert, thus preventing plasticdrooling.4. Metal-to-metal seals based on high molten plastic pressure are usedbetween back tapered extensions and primary sprue bar, front taperedextensions and primary sprue bar, and the front floating sprue insertand the shank on the shut-off valve. The sealing ability of themetal-to-metal seals improves with the higher pressure of the moltenplastic, coinciding with the need for an improved sealing to limit theleaks of the molten plastic.5. Wiper seal which improves its sealing performance with increasedtemperature is used to further limit molten plastic leaks.6. Weep holes are provided to discharge the molten plastic which leakedpast the metal-to-metal seals and the wiper seal.7. Recirculation area is reduced by increasing the diameter of frontfloating sprue insert in the vicinity of the back tapered extension.8. Two-part “C” clamp uses one fastener only to attach each part withthe front floating sprue. The removal of the “C” clamp provides an easyaccess to the front floating sprue insert, primary sprue shut-off insertand the parts attached thereto.

A fifth alternate embodiment of the invention is shown in connectionwith FIGS. 36-37, and is described below. According to one aspect of thefifth alternative embodiment, the crossover nozzle system does not havea primary sprue shut-off valve. The molten plastic has an uninterruptedpath from the inlet hole in the primary sprue bar to the hole in theprimary sprue shut-off insert. Some level of the molten plastic drool istolerated at the hole in the primary sprue shut-off insert. Therefore,the crossover nozzle system of this embodiment may be well suited forthe molten plastics having high viscosity and high surface tension,because those properties reduce the leaks. The pressure of the moltenplastic is regulated by, for instance, turning the molten plastic feeddrive on and off, and by opening and closing the molds.

Furthermore, the fifth alternative embodiment incorporates theadvantages of the metal-to-metal sealing, the wiper seal, a reducedrecirculation flow, easily removable “C” clamp design, and a singlesprue bar. These advantages are explained in detail with the fourthembodiment shown in FIGS. 33-35, and are not repeated here for the sakeof brevity.

FIG. 36 shows crossover nozzle system 1400 in accordance with the fifthembodiment of the invention. Other parts of the mold, like the topplate, feeder plate/stationary core plate, stationary core, moldcavities, manifold plates, cavity plates, core plates, bottom plates,etc., are described in connection with the other embodiments disclosedin this application, and are not shown in FIG. 36. Furthermore, while asingle crossover nozzle assembly is shown in FIG. 36, it would be clearto a person skilled in the art of injection molding that multiplecrossover nozzle assemblies may be used, both in a central and theoff-center positions.

Referring to FIG. 36, a molten plastic feed drive (not shown) forces themolten plastic into inlet hole 1424, and, from there, into the spacebetween front floating sprue insert 1422 and primary sprue bar 1410.From there, one or more radial holes 1456 lead to sprue insert hole1484, and further to opening 1454 on primary sprue shut-off insert 1444,and further to the molds. When the molten plastic feed drive is on, thehigh pressure of molten plastic improves metal-to-metal sealing, thusreducing the leaks (as explained in detail above with reference to FIGS.33-35). When the molten plastic drive is off, the pressure of the moltenplastic is reduced, but a certain amount of drool may occur at opening1454, because this crossover nozzle system does not have a shut-offvalve. Thus, the crossover nozzle system as in FIG. 36 may be suitablefor the high viscosity and/or high surface tension molten plastics.

FIG. 37 shows the path of molten plastic (depicted by the shading)through crossover nozzle system 1400. The molten plastic enters inlethole 1424, and flows to radial holes 1456, and from there to sprueinsert hole 1484 and further to opening 1454. FIG. 37 is across-sectional view having the cross-section plane passing through oneof radial hole 1456 on the left hand side. Additional radial holes 1456may be present, but, not being on the cross-section plane, are not shownin FIG. 37.

The crossover nozzle system in general and that of the fifth alternativeembodiment described above provides the following advantageous features:

1. There is no shut-off valve. Therefore, no actuation of the valve isneeded, either by the molten plastic pressure or by the externalactuators. Certain level of the molten plastic drool is tolerated inthis embodiment.2. Primary sprue bar is one-piece. Primary sprue bar extension is notneeded, thus a design simplification is achieved.3. Metal-to-metal seals based on high molten plastic pressure are usedbetween back tapered extensions and primary sprue bar, front taperedextensions and primary sprue bar, and the front floating sprue insertand the shank on the shut-off valve. The sealing ability of themetal-to-metal seals improves with the higher pressure of the moltenplastic, coinciding with the need for an improved sealing to limit theleaks of molten plastic.4. Wiper seal which improves its sealing performance with increasedtemperature is used to further limit molten plastic leaks.5. Weep holes are provided to discharge the molten plastic which leakedpast the metal-to-metal seals and the wiper seal.6. Recirculation area is reduced by increasing the diameter of frontfloating sprue insert in the vicinity of the back tapered extension.7. Two-part “C” clamp uses one fastener only to attach each part withthe front floating sprue. The removal of the “C” clamp provides an easyaccess to the front floating sprue insert, primary sprue shut-offinsert, and the parts attached thereto.

As will be understood by those skilled in the art, the present inventionmay be embodied in other specific forms without departing from theessential characteristics thereof. These other embodiments are intendedto be included within the scope of the present invention, which is setforth in the following claims.

1. A crossover nozzle system for transferring molten plastic from afeeder manifold to a main manifold of the molding chambers of the stackmolds of an injection molding machine, the system comprising: a primarysprue bar having an aperture in fluid communication with the feedermanifold; a front floating sprue insert having a central aperture andurging means housed in the central aperture; a transfer chamber formedbetween the front floating sprue insert and the primary sprue bar, saidtransfer chamber in fluid communication with the aperture in the primarysprue bar and with one or more radial apertures in the front floatingsprue insert; a shut-off valve having a first end and a second end, saidfirst end of the shut off valve being slidably housed in the centralaperture of the front floating sprue and being biased by the urgingmeans; and a primary sprue shut-off insert having an aperture in fluidcommunication with the one or more radial apertures in the frontfloating sprue insert, wherein: said shut-off valve having a non-uniformdiameter in contact with molten plastic, said non-uniform diameter beingconfigured to create a bias force based on a pressure of molten plastic,said second end of the shut-off valve being configured to disengage froman opening on the front floating sprue insert when the pressure ofmolten plastic overcomes the force of said biasing means, thus openingflow of molten plastics to the molds, and said second end of theshut-off valve being configured to engage with an opening on the frontfloating sprue insert when the force of said biasing means overcomes thepressure of molten plastic, thus closing flow of molten plastics to themolds.
 2. The crossover nozzle system of claim 1, further comprising acollar disposed around said shut-off valve, said collar configured toform a metal-to-metal seal with said front floating sprue insert,wherein said metal-to-metal sealing improves with a pressure of moltenplastic.
 3. The crossover nozzle system of claim 1, further comprising aback floating sprue sleeve having a back tapered extension configured toform a metal-to-metal seal with said primary sprue bar, wherein saidmetal-to-metal sealing improves with a pressure of molten plastic. 4.The crossover nozzle system of claim 1, further comprising a frontfloating sprue having a front tapered extension configured to form ametal-to-metal seal with said primary sprue bar, wherein saidmetal-to-metal sealing improves with a pressure of molten plastic. 5.The crossover nozzle system of claim 1, further comprising a wiper sealdisposed between the primary sprue bar and the back floating spruesleeve and configured to reduce molten plastic leaks between the primarysprue bar and the back floating sprue sleeve.
 6. The crossover nozzlesystem of claim 1, further comprising one or more weep holes disposed onthe primary sprue bar, said weep holes configured to drain moltenplastic out of the system.
 7. The crossover nozzle system of claim 1,further comprising a two-part “C” clamp configured to attach to a frontfloating sprue using one fastener per “C” clamp part, thus enabling easyaccess to the shut-off valve.
 8. The crossover nozzle system of claim 1,wherein the diameter of the front floating sprue insert is dimensionedto reduce a space between the front floating sprue insert and the backtapered extension, thus reducing a recirculation area for the moltenplastic flow.
 9. The crossover nozzle system of claim 1, furthercomprising a seal disposed between the primary sprue bar and the frontfloating sprue, said seal configured to reduce molten plastic leaksbetween the primary sprue bar and the front floating sprue.
 10. Acrossover nozzle system for transferring molten plastic from a feedermanifold to a main manifold of the molding chambers of the stack moldsof an injection molding machine, the system comprising: a primary spruebar having an aperture in fluid communication with the feeder manifold;a front floating sprue insert having a central aperture and one or moreradial apertures, said central aperture in fluid communication with saidone or more radial apertures; a transfer chamber formed between thefront floating sprue insert and the primary sprue bar, said transferchamber in fluid communication with the aperture in the primary spruebar and with the one or more radial apertures in the front floatingsprue insert; and a primary sprue shut-off insert having a first end anda second end, said first end in fluid communication with the one or moreradial apertures in the front floating sprue insert, said second end influid communication with the molds, wherein a flow of molten plastic atsaid second end is controlled in absence of a shut-off valve in theprimary sprue shut-off.
 11. The crossover nozzle system of claim 10,further comprising a back floating sprue sleeve having a back taperedextension configured to form a metal-to-metal seal with said primarysprue bar, wherein said metal-to-metal sealing improves with a pressureof molten plastic.
 12. The crossover nozzle system of claim 10, furthercomprising a front floating sprue having a front tapered extensionconfigured to form a metal-to-metal seal with said primary sprue bar,wherein said metal-to-metal sealing improves with a pressure of moltenplastic.
 13. The crossover nozzle system of claim 10, further comprisinga wiper seal disposed between the primary sprue bar and the backfloating sprue sleeve, said wiper seal configured to reduce moltenplastic leaks between the primary sprue bar and the back floating spruesleeve.
 14. The crossover nozzle system of claim 10, further comprisingone or more weep holes disposed on the primary sprue bar, said weepholes configured to drain molten plastic out of the system.
 15. Thecrossover nozzle system of claim 10, further comprising a two-part “C”clamp configured to attach to a front floating sprue with one fastenerper “C” clamp part, thus enabling easy access to the shut-off valve. 16.The crossover nozzle system of claim 10, wherein the diameter of thefront floating sprue insert is dimensioned to reduce a space between thefront floating sprue insert and the back tapered extension, thusreducing a recirculation area for the molten plastic flow.
 17. Thecrossover nozzle system of claim 10, further comprising a seal disposedbetween the primary sprue bar and the front floating sprue, said sealconfigured to reduce molten plastic leaks between the primary sprue barand the front floating sprue.